Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
  • G01R1/02—General constructional details
  • G01R1/06—Measuring leads; Measuring probes
  • G01R1/067—Measuring probes
  • G01R1/06788—Hand-held or hand-manipulated probes, e.g. for oscilloscopes or for portable test instruments
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
  • G01R1/20—Modifications of basic electric elements for use in electric measuring instruments; Structural combinations of such elements with such instruments
  • G01R1/22—Tong testers acting as secondary windings of current transformers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
  • G01R1/02—General constructional details
  • G01R1/04—Housings; Supporting members; Arrangements of terminals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
  • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
  • G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers

Definitions

• This invention generally relates to electronic test tools, and more specifically, to a current clamp meter having a detachable current clamp that can be used to measure current with the current clamp attached or detached from the meter.
• Electrical current can be measured by connecting a current meter in series with the wire.
• disconnecting the wire to connect the current meter can be inconvenient.
• the wire can be tightly grouped in a bundle with several other wires making it difficult to individually disconnect the wire of interest.
• Another example of the inconvenience is where a terminal to which the wire is connected is not conveniently located or is inaccessible, requiring the wire to be cut for the current meter to be connected in series. It is time consuming to reconnect the two ends of the cut wire after a measurement is taken, and can be dangerous in situations where relatively high current is carried by the wire. Additionally, the integrity of the wire is compromised by cutting and reconnecting, thus, potentially raising reliability problems.
• a clamp probe connected to a conventional multimeter can be used to measure electrical current without the need for disconnecting a wire.
• the clamp probe is opened, the wire is inserted into the clamp, and the clamp is closed to take a current measurement.
• the closed clamp includes a core of ferromagnetic material, which when closed, represents the core of a transformer.
• the wire passing through the clamp represents the primary winding.
• a current flowing in the wire induces a magnetic flux in the core of the transformer, which in turn, induces a current in a secondary winding of the transformer.
• the magnitude and polarity of the current in the clamped wire can be determined based on the current induced in the secondary winding and the characteristics of the transformer formed by the clamped wire.
• a clamp probe can be connected to a multimeter having current measuring capabilities for taking current measurements.
• the clamp probe is typically connected to the multimeter through wires that connect to plug-in terminals.
• a benefit to this arrangement is that the clamp probe can be clamped to the wire and the meter positioned so that a technician can conveniently view the measured value, which is especially useful when the wire is located in a difficult to reach location.
• two hands are typically necessary to take a measurement: one to put the clamp in place and another to hold the meter while taking a measurement.
• the clamp probe is an attachment to the multimeter, it is typically stored separately from the meter, which can be inconvenient when carrying the equipment around and can also be easily misplaced when not used.
• clamp meters are designed with the clamp integrated into the body of the meter, which can provide the convenience of taking a measurement using one hand. That is, only one hand is used to open and close the clamp for clamping a wire and to take a current reading. Additionally, with the clamp integrated into the body of the meter, there is no possibility of misplacing the clamp or having any difficulties transporting the equipment.
• One-handed clamp meters are generally acceptable for applications where the display can be easily viewed by the technician with the meter clamped to the wire for measurement.
• problems with reading the measurement can arise where the wire is difficult to reach or is positioned such that the display of the meter is obscured when the meter is in position for measurement.
• a technician can quickly check the display by forcing himself into an awkward position just long enough to view the display, or where the meter has a feature which captures a measured value on a display, the technician can remove the meter from the awkward or obscured position after the measurement is taken and view the captured measured value.
• the technician must put himself in a physically uncomfortable and potentially dangerous position when attempting to view the measured value on the display of an awkwardly positioned meter.
• removing the meter from a wire that was difficult to clamp in the first place is inconvenient and can be time consuming if the clamp meter must be re-clamped to take additional measurements from the same wire.
• real time measurements such as measuring start-up currents or detecting intermittent current loading, the meter must be kept in place during continuous measurement.
• a meter having a remote clamp probe such as using a clamp probe coupled to a multimeter as previously described, can be used to address the problems with awkward to reach or difficult positioned wires by clamping the wire with the remote clamp, and having the meter positioned in a convenient location for reading the measured values.
• these meters also lack the convenience of one-handed measurements for applications where it is possible to do so.
• a solution to the problem is for a technician to have both types of meters in order to have the benefits of each design. This is a costly solution since two different meters need to be purchased, although only one meter is typically used at a time for taking a measurement.
• One aspect of the invention provides a current clamp meter having a current meter body and a current clamp.
• the current meter body includes circuits operable to calculate a current measurement from an input signal and the current clamp is electrically coupled to the circuits included in the current meter body to sense a current and provide the input signal.
• the current meter body and the current clamp are configured to have the current clamp detachable from the current meter body so that the current clamp meter can be operated with the current clamp either attached to the current meter body or detached from the current meter body.
• a handheld electrical measuring instrument that includes a current probe and an instrument housing.
• the housing has a probe retention member configured to receive and detachably retain the current probe and further configured to allow the current probe to be detached from the probe retention member and used either retained by or detached from the probe retention member.
• Another aspect of the invention provides a method for operating a current clamp meter.
• the method includes detaching a current clamp probe releasably attached to a housing of the current clamp meter and attaching the current clamp probe to a first conductor. A first current in the first conductor is measured.
• the method further includes reattaching the current clamp to the housing of the current clamp meter, attaching the current clamp while attached to the housing to a second conductor, and measuring a second current in the second conductor.
• Figures IA and IB are isometric drawings of a clamp meter according to an embodiment of the present invention having a current clamp nested in the body of the meter.
• Figures 2A and 2B are isometric drawings of the clamp meter of Figures IA and
• FIG. 3 is a simplified block diagram of the clamp meter according to an embodiment of the present invention.
• Figures 4A and 4B illustrate the use of a clamp meter according to an embodiment of the present invention with the current clamp attached.
• Figure 5 illustrates the use of a clamp meter according to an embodiment of the present invention with the current clamp detached.
• FIGS IA and IB illustrate a clamp meter 100 according to an embodiment of the present invention.
• the clamp meter 100 includes a current clamp probe 110 that is detachable from a housing 112 in which circuitry for the clamp meter 100 are encased.
• the clamp probe 110 includes a current sensor for detecting current in a wire positioned in an opening 111. Examples of current sensors include Hall-effect devices and coils such as a current transformer, as known in the art.
• the clamp probe 110 is positioned in a recess 120 generally defined by clamp retention members 122, 126 that extend from a body 114.
• the clamp retention members 122, 126 have respective cutouts 124, 128 to expose a lever portion 130 of the clamp probe 110.
• the lever portion 130 causes jaws of the clamp probe 110 to open to receive a wire in the opening 111 for measurement.
• the clamp probe 110 is a spring loaded device whereupon release of the lever portion 130, the clamp probe 110 will close. Consequently, when the wire is positioned in the opening 111, the lever portion 130 can be released to capture the wire for measurement.
• a wire can be released from the opening 111 by depressing the lever portion 130 and withdrawing the meter 100.
• An interior surface of each of the clamp retention members 122, 126 can optionally include a guide 118 for facilitating placement of the clamp probe 110 in the recess 120.
• the clamp probe 110 abuts the guide 118 when correctly positioned in the recess 120.
• the guide 118 can be further configured to keep the clamp probe 110 from moving when pressure is applied to the lever portion 130.
• the clamp retention members 122, 126 can include optional ridges 127 to provide tactile indicators of a known distance from the opening 111 when the clamp probe 110 is positioned in the recess 120.
• the clamp probe 110 can be retained by the clamp retention members 122, 126 using known techniques, such as an interference fit, snap fit, or the like, between the clamp probe 110 and the clamp retention members 122, 126.
• the technique used is sufficient to hold the clamp probe 110 in place when pressure is applied to the lever portion 130 while still allowing removal from the clamp retention members 122, 126.
• a user interface for receiving input from and providing information to a user.
• the user interface shown in Figure IA includes a display 132 for displaying information, such as a measured value, mode of operation, and device and battery status.
• the user interface further includes buttons 134 that can be used to receive input from the user and carry out functions in the meter, for example, turning the meter on and off, selecting a mode of operation, selecting a measurement range, and taking a measurement.
• buttons 134 additional or alternative user input devices can be used in other embodiments, such as dials, thumb wheels, and switches. Additionally, the user input devices can be located at different positions than shown in Figure IA.
• An optional light 140 can be included on the body 114 and positioned to provide illumination in the direction of the clamp probe 110 to aid in locating and clamping a wire in a darkened environment.
• the light 140 can use a conventional light source, such as a filament-based light source and a light emitting diode (“LED”) light source. Other types of light sources can be used as well.
• the light 140 can be designed to be switched on and off using one of the buttons 134.
• the clamp probe 110 is electrically coupled to circuitry enclosed by the housing
• Figure 3 illustrates a simplified block diagram of electrical circuits that can be included in the clamp meter 100.
• the electrical circuits shown in Figure 3 are provided by way of example.
• the circuits included in the clamp meter 100 can be implemented in the meter 100 using conventional designs and operation.
• the clamp probe 110 is electrically coupled to a connector 310 through the wire
• a processor 330 receives the conditioned signal and computes a current measurement.
• the processor 330 generates signals to drive a liquid crystal display (“LCD”) 132 to display information, including the computed current value.
• LCD liquid crystal display
• ADC analog-to-digital converter
• Buttons 134 are provided for user input to the processor 330.
• a power supply 340 provides power to various circuitry of the meter 100, such as the signal conditioning circuit 320, the processor 330, and the LCD 132.
• the power supply 340 typically includes a battery and power circuits for regulating the provision of power to the circuits in the meter 100.
• the processor 330 is operable to compute measurements for other electrical characteristics, as detected by test probes coupled to electrical terminals (not shown) further included in the connector 310.
• multimeter functionality can be integrated into the meter 100, such as measuring voltage and resistance.
• the wire 116 can be neatly stowed to prevent tangling by wrapping the wire 116 around a rear portion 150.
• the rear portion is configured to form recesses 156 into which the wire 116 is received when wrapped.
• An optional groove 160 can be included in the body 114 for holding the wire 116 in place when wrapped around the rear portion 150 and the clamp probe 110 is positioned in the clamp retention members 122, 126.
• the rear portion 150 is removable to provide access to the electronics of the meter 100, such as for removal and installation of a battery or to allow for calibration.
• the rear portion 150 is integral with the rest of the housing 112.
• FIGS 2A and 2B illustrate the meter 100 with the clamp probe 110 detached from the housing 112 and the wire 116 fully deployed.
• the clamp probe 110 includes a ridge 129 to provide a tactile indicator of a known distance from the opening 111 when the clamp probe 110 is detached from the housing 112.
• the jaws of the clamp probe 110 can be opened by applying opposing pressure to the lever portion 130 and an opposite lever portion 131. As previously discussed, the clamp probe 110 is spring loaded, and upon release of the lever portion 130 and the opposite lever portion 131, the jaws of the clamp probe 110 will close.
• the meter 100 can be used with the clamp probe 110 positioned in the recess 120 or with the clamp probe 110 detached. Consequently, the convenience and functionality of the two conventionally configured clamp probe/meters are combined in one clamp meter.
• FIGs 4A and 4B illustrate operation with the clamp probe 110 in place between the clamp retention members 122, 126.
• clamping a wire 410 and taking a measurement can be accomplished with one-handed operation.
• the clamp probe 110 can be operated by pressing the lever portion 130 using the thumb or a finger of one hand in order to clamp the wire 410.
• the lever portion 130 is released, as shown in Figure 4B, the clamp probe 110 captures the wire 410.
• buttons 134 can be pressed using the thumb or fingers of the same hand during measurement.
• One-handed operation is convenient for situations where the display 132 is viewable when the wire is clamped and the wire is easily accessible.
• the clamp probe 110 detached. With the clamp probe 110 detached from the housing 112 and the wire 116 unwrapped from the rear portion 150, the clamp probe 110 can be clamped to a wire 420 in an awkward location and the housing 112 positioned so that the display 132 is easily viewable. In this manner, it is unnecessary to remove the meter 100 from the clamped wire 420 after an initial measurement is taken, saving time and effort where subsequent measurements from the same wire are to be taken.
• the clamp probe 110 is illustrated as being slightly tapered to a "nose," which facilitates clamping of a wire that may be bundled with other wires.
• other shaped clamp probes can be used in alternative embodiments.
• a clamp probe having more arcuate shaped jaws or having a larger opening can be used to accommodate larger diameter wires or used for applications where individual wires are sufficiently spaced and can be easily clamped.
• Even with differently shaped clamp probes the option of taking a measurement with the clamp probe attached for one-handed operation or taking a measurement with the clamp probe detached is still desirable since the dual-use configuration allows the display to be conveniently positioned during measurement.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Measuring Instrument Details And Bridges, And Automatic Balancing Devices (AREA)
• Measurement Of Current Or Voltage (AREA)

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Citations (5)

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• 2006
  • 2006-04-27 US US11/414,655 patent/US7439726B2/en active Active
• 2007
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  • 2007-04-12 WO PCT/US2007/066519 patent/WO2007127617A2/en active Application Filing
  • 2007-04-12 CN CNA2007800210510A patent/CN101467052A/zh active Pending
  • 2007-04-12 BR BRPI0710766-8A patent/BRPI0710766B1/pt active IP Right Grant
  • 2007-04-12 JP JP2009507889A patent/JP5039778B2/ja active Active
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